A gas turbine engine typically includes a compressor, a combustor, and a turbine section. The compressor and turbine section may generally include rows of airfoils or blades that are axially stacked in stages. Each stage generally includes a row of circumferentially spaced stator blades or nozzles which are fixed in position, and a set of circumferentially spaced rotor blades, that rotate about a central axis or shaft. In operation, the rotor blades in the compressor rotate about a rotor shaft to compress a flow of air. The supply of compressed air may be combined with a fuel to form a combustible mixture within a combustion zone of the combustor. The combustible mixture is burned to provide a rapidly expanding hot gas. The resulting flow of hot gas expands through the turbine section, which causes the turbine rotor blades to rotate about the rotor shaft and/or a turbine shaft. In this manner, energy from the hot gases may impart kinetic energy to the blades of the turbine section, thereby causing the rotor shaft and/or the turbine shaft to rotate. The rotating shaft may be used to drive a load such as a generator to generate electricity.
In some gas turbines, adjacent stages of stator blades may be configured with substantially the same number of circumferentially spaced stator blades. In addition or in the alternative, adjacent stages of rotor blades may be configured with substantially the same number of circumferentially spaced rotor blades. In an effort to improve the aero-efficiency, efforts have been made to index or “clock” the circumferential positions of the stator and/or rotor blades in one stage relative to the circumferential position of the stator and/or rotor blades in nearby or neighboring stages.
Various methods for determining an optimized clocking angle between adjacent stages of stator and/or rotor blades currently exist. However, it has been discovered that such conventional clocking methods may increase the mechanical stresses acting on certain airfoils during operation. Clocking angles may be generally determined during a design or a redesign phase of the gas turbine section by using steady and unsteady state computational fluid dynamic (CFD) computer modeling. For example, current design methods may generally model a baseline fluid flow profile across three or more alternating rows of adjacent stator and/or rotor blades. In particular, the model may be used to determine various parameters from the fluid flow profile such as wake formation and wake shape of the fluid as it flows from a trailing edge of a second row of the blades downstream towards the leading edge of an adjacent third row of the blades. As a result, designers may then clock the third row of blades based on the modeled fluid flow profile so as to optimize the fluid flow through the compressor and/or the turbine section.
The primary issue is that actual clocking generally takes place during assembly of the gas turbine. Therefore, once the various stages of stator blades and/or rotor blades have been clocked into a certain position and the gas turbine fully assembled, modification of the clock angles of the various stages of the stator and/or rotor blades so as to improve the thermal, mechanical and/or the aerodynamic performance of the gas turbine may be generally impractical. As a result, undesirable mechanical stresses on the airfoils and/or undesirable effects on gas turbine performance may be too difficult and/or too expensive to mitigate. Therefore, a new method for enhancing the performance of a gas turbine with fixed clocked stages of stator blades and/or rotating blades would be useful.